Multilayer propping of fractures

ABSTRACT

A method for increasing the permeability of a formation whereby alternate layers of substantially insoluble particles (propping agent) and essentially soluble particles are emplaced in a fracture in said formation. At least one of the layers of substantially insoluble particles is treated with a stabilizing resin which can be hardened or otherwise set up to physically stabilize that layer to resist movement of the insoluble particles back toward the wellbore during the production of fluid through the fracture and into the wellbore.

United States Patent 1191 Kern et al.

1451 Sept. 11, 1973 MULTILAYER PROPPING OF FRACTURES [75] Inventors:Loyd R. Kern; Ferman G. Martin,

both of Irving, Tex.

22 Filed: 'Au .1'1,1972

211 App]. No; 279,879

[52] US. Cl 166/280, 166/281, 166/295 [51] Int. Cl. E2lb 33/138, E2lb43/26 [58] Field of Search 166/280, 276, 295, 166/308, 281

[56] References Cited UNITED STATES PATENTS 2,823,753 2/1958 Hendersonet a1 166/276 X 2,981,334 4/1961 Powell, Jr. 166/276 2,986,538 5/1961Nesbitt et al. 166/295 X 3,123,137 3/1964 Young et al. 166/295 3,127,9374/1964 McGuire, Jr. et al. 166/281 X 3,155,159 11/1964 McGuire, Jr. etal. 166/280 3,235,007 2/1966 Kern et al. 166/280 3,285,339 11/1966Walther et al. 166/295 3,297,086 l/l967 Spain 166/295 3,443,637 7 5/1969Sparlin et al 166/295 Primary Examiner-Stephen J. NovosadAtzorneyRoderick W. MacDonald et al.

[5 7] ABSTRACT A method for increasing the permeability of aformation'whereby alternate layers of substantially insoluble particles(propping agent) and essentially soluble particles are emplaced in afracture in said formation. .At least one of the layers of substantiallyinsoluble particles is treated with a stabilizing resin which can behardened or otherwise set up to physically stabilize that layer toresist movement of the insoluble particles back toward the wellboreduring the production of fluid through the fracture and into thewellbore.

20 Claims, No Drawings Heretofore, it has been taught to employ inan'upright or otherwise vertically oriented fracture in a sub surfaceformation of the earth, alternate layers of substantially insoluble andessentially soluble particles after which the layer or layers of solubleparticles are dissolved by the passage of a solvent through thefracture. This leaves a fracture which is propped open by a plurality ofsubstantially horizontally disposed bridges of insoluble material, thebridges having void spaces therebetween where the soluble material onceexisted. This process is fully and completely disclosed in US. Pat. No.3,235,007, the disclosure of which is incorporated herein by reference.

As taught in the above-cited patent, the alternate layers of soluble andinsoluble particles can be deposited in the fracture either by flotationor by gravity settling or both, these processes being fully andcompletely dis closed in US. Pat. Nos. 3,155,159 and 3,127,937, thedisclosures of which are incorporated herein by reference.

It has been found that in some cases, even though the remaininginsoluble layers are under substantial .compressive force actingsubstantially perpendicular to the plane of the fracture, such forcebeing sufficient to close the fracture but for the presence of theinsoluble layers, a substantial amount of the insoluble particles can bewashed from the fracture into the wellbore by DETAILED DESCRIPTION OFTHE INVENTION By this invention, a fracture is initiatedoutwardly from awellbore into a formation in the conventional manner by introducing afracturing fluid into the wellbore and increasing the pressure on saidfracturing fluid until a crack in the formation is formed and widened tothe desired width. While the fracture is main-'- tained in its openposition by the pressurized fracturing fluid, propping agent isintroduced thereinto so that thereafter when the pressure on thefracturing fluid is reduced the naturally-occurring forces in theformation subsequent normal production of fluid from the formationthrough the fracture and into the wellbore. This is undesirable becausesubstantial amounts of these insoluble particles can be deposited in thewellbore and/or find their way into downhole tools andequipment andcause problems or even breakdown in the operation of these tools andequipment.

SUMMARY OF TI-IE INVENTION According to this invention, there isprovided a method whereby the alternate layers of soluble and insolubleparticles are emplaced in a substantially upright fracture which extendsfrom a wellbore into a subsurface earth formation and one or more of theinsoluble particle layers is treated with astabilizing resin which canbe set up'after emplacement of the insoluble particles in the fracture.The stabilizing resin is set up to physically stabilize the treatedinsoluble particle layer to resist movement of the insoluble particlesof that layer towardth e wellbore during subsequent production of fluidthrough the fracture into the wellbore.

Accordingly, it'is an object of this invention to provide a new andimproved fracturing method. It is another object to provide new andimproved method for increasing the permeability of a subsurface earthformation to fluid. It is another object to provide anew and improvedmethod for establishing high conductivity fractures in a subsurfaceearth formation. It is another object to provide a new and improvedmethod for establishing a propped fracture wherein the propping agent inthe fracture has at least one open channel therethrough, the proppingagent in the fracture resisting movement from said fracture into thewellbore.

Other aspects, objects and advantages of this invention will be apparentto those skilled in the art-from this disclosureand the appended claims.

once again become paramount and, but for the propping agent, would forcethe fracture completely closed. The propping agent in the fracture thusprevents complete closing thereof and thereby maintains the permeabilityachieved in the first place by the fracturing process. This inventionapplies to any conventional processing technique. The process can use asa carrier fluid for the propping agents an aqueous base liquid or an oilbase liquid. The fracturing fluid can also contain any conventionalmaterial for fracturing fluidssuch as viscosity, thickening, or gellingagents and the like.

As noted hereinabove, this invention employs the technique of US. Pat.No. 3,235,007 in the emplacement in the fracture of alternate layers ofsoluble and either a fluid which will normally be produced from theformation through the fracture to the wellbore or which can beintroduced into the fracture from the earths surface by way of thewellbore so long as substantial dissolution of the soluble particles inthe fracture is obtained. Thus, the soluble particles could be solublein hydrocarbonaceous materials or in aqueous materials depending uponthe composition of the fluids that are normally produced from theparticular well and upon the desired composition for the fracturingfluid. Suitable soluble and insoluble materials are fully and completelydisclosed in US. Pat. No. 3,235,007. One or more types of insolubleparticles can be used in any given layer. The same is true for any givensoluble layer.

In this invention, for example, a first layer of insoluble particles islaid down in the fracture after which the next adjacent layer to saidfirst layer will be soluble particles. Thereafter, the next adjacentorthird layer will be a layer of insoluble particles after which the nextadjacent or fourth layer will be of soluble particles and so on asdesired. The minimum requirement is two layers of insoluble particlesspaced apart by an intermediate layer of soluble particles, there beingno maximum number of alternating layers except that which is dic-,

'tated by the physical size of the fracture itself.

According to this invention, at least one of the layers of insolubleparticles in the fracture is'treated with a V stabilizing resin. Thetreatment of a. particular layer of insoluble particles can take placeafter the soluble and insoluble layers have been emplaced and thesoluble layers dissolved. A more useful technique is to first mix lizingresin with the insoluble particles absent the carrier fluid. By theprior mixing approach, the resin and insoluble particles travel down thewellbore and into the fracture together, the resin and insolubleparticles being intimately mixed with one another before and/or duringtheir travel together. The mixture is then emplaced in the fracture. Inthis way, a good intimate mixture of particles and resin is achieved andthe next slug of carrier fluid containing soluble particles for the nextadjacent layer can follow up the first slug with substantially no losttime. Catalyst can also be mixed with the resin and insoluble particleson the earths surface and then introduced into the fracture. The settingof the resin can then be triggered by heating, e.g., geothermal.heating.

it can be desirable, especially when mixing resin and insolubleparticles together on the earths surface, to incorporate in any mixtureof resin and insoluble particles an effective amount of at least onecoupling agent which strengthens the bond between the resin andinsoluble particles and/or makes the insoluble particles resin wet.Suitable coupling agents are known in the art and are fully andcompletely disclosed in U.S. Pat. Nos. 3,282,338; 3,297,086; 3,404,735;and 3,443,386, the disclosures of which are incorporated herein byreference.

A particularly desirable procedure is' to mix the insoluble particleswith resin and coupling agent in a hydrocarbon oil and to separately mixthe soluble particles in water. In this way, after emplacement of thevarious layers, the resin is less likely to flow from one layer ofinsoluble particles to an adjacent layer of soluble particles.

Thus, it is preferred that one or more of the resins in liquid orparticulate form be physically mixed with the insoluble particles andone or more coupling agents on the earth s surface and this mixturedispersed in a carrier fluid which is to form the slug from transmittingthe insoluble particles from the earths surface into the fracture. a

The resin can be set up either by being subjected to heat or the actionof a catalyst or both. The heat can come from the earth as geothermalheat, or as external heat from the surface of the, earth such as bypumping steam down the wellbore, or both as desired and convenient. Thecatalyst or curing agent can be supplied from the earths surface throughthe wellbore or, depending upon the composition of the naturallyoccurring fluid in the well, can come from the fractured formationitself, or both as desired and available. Combinations of heat andcatalyst can also be employed such as in the situation where thestabilizing resin is a thermosetting resin and there is some but notsufficient geothermal heat available and it is more convenient tointroduce a catalyst which when combined with the geothermal heatpresent in the formation is sufficient to cause the resin to set up tothe desired extent. Thus,

the resin is normally set up after the layer emplacing procedure iscompleted and during and/or after dissolving the soluble layers. Forexample, with certain resinshydrochloric acid can be used to dissolvethe soluble layers and at the same time act as a catalyst to set up theresin. Alternatively, the soluble layers can be dissolved after whichthe resin is treated to set it up.

Suitable thermosetting and/or catalytic setting resins include phenolicresins such as hydroxy arylaldehyde condensation products; hydroxyalkylaryl aldehyde condensation products and the like; urea aldehyde;amine aldehyde; acrylic resin such as those prepared from methylmethacrylate, ethylacrylate, n-butyl methacrylate, isobutylmethacrylate, ethyl methacrylate and similar esters, alone or incombination with other monomers; vinyl resins such as those preparedfrom vinyl chloride, vinyl acetate, vinyl alcohol, vinyl acetal, vinylbutyral, vinyl formal, vinylidene chloride, and the like; allyl resinssuch as allyl diglycol carbonate; alkyl resins such as glycerylphthalate and the like; furan resins; polyepoxide resins such as thosefully and completely disclosed in U.S. Pat. No. 3,391,738, the disclo-'sure of which is incorporated herein by reference; polyester resins suchas those prepared by the copolymerization of a dihydride alcohol such asethylene glycol, and unsaturated dibasic acids such as fumaric acid andan unsaturated monomer, such as styrene, and the like; polyisocyanateresins such as polyurethane derived from polyisocyanates such as toluenediisocyanate and polyols including gylcols, polyesters and polyethers;silicone resins such as those produced by the hydrolysis andcondensation of organosilanehalide intermediates; styrene resinsincluding both homoplymers and copolymers; furfuryl alcohol resins such.as furfuryl alcohol reacted with formaldehyde, with urea andformaldehyde, with phenol and formaldehyde or with one or more compoundscontaining two or more epoxy groups; and furfural resins. These resinsare either thermosettingor catalytic setting or both. For example,polyepoxides can be set or otherwise hardened by treatment with amines,dibasic acids, acid anhydrides, and the like as fully and completelydisclosed in said U.S. Pat. No. 3,391,738 while the furfural alcoholresins can be set up by treatment with hydrogen chloride, acyl halidessuch as methyl chloride, boron .trifluoride, boron trichloride, sulfurdioxide, hydrogen sulfide, other similar Lewis acids, and thelike.Phenolic resins, aldehyde resins, and the like are therrnosetting butoftentimes can also be treated with a catalyst to promote the setting upprocess. For example, an alkali catalyst such as sodium hydroxide can beadded as a catalyst for these thermo setting resins. The thermosettingresins can, however, generally be set up by subjecting same to heat fora finite period of time in the absence of any catalyst. Preferredstabilizing resins are phenol formaldehyde, urea formaldehyde, andphenol furfural.

The amounts of stabilizing resin or resins employed vary quite widelydepending upon the particular resins used, the particular insolubleparticles used, the amount of insoluble particles used, the method bywhich the resin is to be set up, the desired degree of hardness to beachieved in the final treated insoluble particle layer, and the like.Generally, sufficient resin or resins will be employed so that theinsoluble particles in the final layer will substantially resistmovement toward the wellbore under the action of fluid produced throughthe fracture into the wellbore.

The particular setting up or curing process employed on the resin willvary widely again as well the specifics of that process, i.e., thetemperature to which the resin is heated, the time for which the resinis heated, the amount of catalysts employed, the form of the catalystemployed, and the like. The resins useful in this invention are known inthe art as are their compositions and properties so that one skilled inthe art can determine the amount of resin to be employed and theparticular curing process to be employed once the resin or resins to beused is known. The resins being known and commercially available,further discussion as to them and their curing processes is unnecessaryto inform the art and therefore are omitted.

EXAMPLE A permeable and porous subsurface formation is fractured usingdiesel fuel as the fracturing fluid. After the fracture is formed andwidened to the desired onetenth inch at the wellbore wall, the pressureon the diesel fuel is maintained by continuous addition of diesel fuelunder pressure to the wellbore to replace diesel fuel which leaks offinto the formation.

A slug of diesel fuel containing 7000 pounds of sand (passing a 20-meshsieve and retained on a 40-mesh sieve), 3 gallons of silane couplingagent and 35 gallons of phenolic resin is mixed at ambient temperatureand pressure and then introduced into the wellbore and fracture to forma first lower layer about 12 feet in height of resin-treated sand in thefracture. Thereafter, a second slug of diesel fuel containing 600 poundsof aragonite (a naturally occurring particle-form limestone) is mixedand then introduced into the wellbore and fracture to provide a secondlayer on top of and contiguous with the first layer, the second layerbeing about one foot in height and constituting the layer of solubleparticles. Thereafter, a third slug of diesel fuel is mixed containing3,000 pounds of sand of the same character used in the first slug, 15gallons of phenolic resin, and 1.2 gallons of silane coupling agent.This slug is then introduced into the wellbore and fracture to form alayer about 5 feet in height above and contiguous with the second layer.Thus, the first and second layers of insoluble particles are spacedapart from one another in the fracture by the soluble layer ofaragonite.

After'the desired amount of soluble and insoluble particles areinjected, the pressure of the fracturing fluid is reduced so that thenaturally occurring stresses in the formation take over and tend toforce the two faces of the fracture toward one another thereby puttingthe three layers of particles under substantial compressive force.

' Thereafter, 1000 gallons of percent hydrochloric acid is injected intothe formation and fracture at a low rate so that the fracturewalls arenot forced open to dislodge the particles. The acid serves twofunctions. It dissolves the aragonite second layer thereby leaving anopen conduit about one foot in height in the fracture between the firstand second layers of sand, and-it causes the resin to set up, thusstabilizing the two layers of sand.

1 Normal production of the well is then taken up whereby fluids existingin the formation migrate from the formation into the fracture and flowto the wellbore through the insoluble sand layers as well as the openconduit left by removal of the aragonite.

The flow of fluid through the sand layers and the open conduit issubstantial as to volume and velocity but the sand in the first andthird layers in the fracture is retained in place inspite of the forcesupplied by the produced fluid due to the hardened resin. Thus,substantially none of the sand in the first and third layers is producedback into the wellbore.

Reasonable variations and modifications are possible within thescope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A method for increasing the permeability of a subsurface earthforrnation to fluid, said formation having a wellbore therein and atleast one substantially upright fracture extending from the wellboreinto said formation, said method comprising introducing into saidfracture at least two discrete slugs of a carrier fluid mixed with solidparticles which are substantially insoluble in a preselected fluid tothereby deposit in said fracture at least two layers of saidsubstantially insoluble particles, introducing into said fracture inalternate sequence with said discrete slugs of substantially insolubleparticles at least one slug of a carrier fluid mixed with solidparticles which are essentially soluble in said preselected fluid sothat there is deposited in said fracture alternating layers of saidinsoluble particles and said soluble particles, said carrier fluid forsaid slugs being substantially a nonsolvent for said soluble particles,providing at least one of said layers of insoluble particles with astabilizing resin which can be set up to physically stabilize said atleast one insoluble particle layer to resist movement of said insolubleparticles toward said wellbore during subsequent production of fluidthrough said fracture into said wellbore, setting up said stabilizingresin in said at leastone insoluble particle layer, and removing atleast part of said soluble particles.

2. A method-according to claim 1 wherein each layer of said insolubleparticles is provided with said stabilizing resin before the nextadjacent layer of soluble particles is emplaced in said fracture.

3. A method according to claim 1 wherein said stabilizing resin is athermosetting resin, and setting said resin by heating same afteremplacement of said resin in said fracture.

4. A method according to claim 3 wherein said heating is provided bygeothermal heat.

5. A method according to claim 1 wherein said stabilizing resin is acatalytic setting resin, and setting said resin by treating same with acatalyst after emplacement of said resin in said fracture.

6. A method according to claim 1 wherein said stabilizing resin is acatalytic setting resin, and setting said resin by treating same with acatalyst which also dissolves at least part of said soluble particles.

7. A method according to claim 6 wherein hydrochloric acid is both saidcatalyst and said soluble particle solvent.

8. A method according to claim 1 wherein said insoluble particles,resin, and catalyst are mixed together on the earths surface and thenintroduced into said fracture after whichsaid resin is set up.

' 9. A method according to claim 8 wherein said resin is set up bygeothermal heating in said fracture.

10. A method according to claim 1 wherein said stabilizing resin is botha thermosetting and a catalytic setting resin, and setting said resin bytreating said resin with at least one of heat and catalyst afteremplacement of said resin in said fracture.

11. A method according to claim 1 wherein said stabilizing resin is atleast one resin selected from the group consisting of phenolic resin,urea aldehyde, amine aldehyde, acrylic resin, vinyl resin, allyl resin,alkyl resin, furan resin, polyepoxide resin, polyisocyanate resin,polyester resin, silicone resin, styrene resin, furfuryl alcohol resin,and furfural resin.

12. A method according to claim 11 wherein said at least one resin isset up using at least one of heat and v a catalyst.

13. A method according to laim l 1 wherein said resin and insolubleparticles are intimately mixed with one another in the absence ofcarrier fluid to resin wet the insoluble particles with said resinbefore said insoluble particles are exposed to said carrier fluid.

14. A method according to claim 13 wherein said resin and insolubleparticles are mixed in the presence of an effective amount of at leastone coupling agent and in the absence of said carrier fluid;

15. A method according to claim 1 wherein said stabilizing resin ismixed with said insoluble particles on the earth s surface beforeemplacement of said insoluble particles into said fracture. V

16. A method according to claim 15 wherein said mixture of resin andinsoluble particles is additionally mixed with carrier fluid beforeemplacement into said fracture. v

17. A method according to claim 15 wherein said resin is mixed with bothsaid insoluble particles and an least one coupling agent.

2. A method according to claim 1 wherein each layer of said insolubleparticles is provided with said stabilizing resin before the nextadjacent layer of soluble particles is emplaced in said fracture.
 3. Amethod according to claim 1 wherein said stabilizing resin is athermosetting resin, and setting said resin by heating same afteremplacement of said resin in said fracture.
 4. A method according toclaim 3 wherein said heating is provided by geothermal heat.
 5. A methodaccording to claim 1 wherein said stabilizing resin is a catalyticsetting resin, and setting said resin by treating same with a catalystafter emplacement of said resin in said fracture.
 6. A method accordingto claim 1 wherein said stabilizing resin is a catalytic setting resin,and setting said resin by treating same with a catalyst which alsodissolves at least part of said soluble particles.
 7. A method accordingto claim 6 wherein hydrochloric acid is both said catalyst and saidsoluble particle solvent.
 8. A method according to claim 1 wherein saidinsoluble particles, resin, and catalyst are mixed together on theearth''s surface and then introduced into said fracture after which saidresin is set up.
 9. A method according to claim 8 wherein said resin isset up by geothermal heating in said fracture.
 10. A method according toclaim 1 wherein said stabilizing resin is both a thermosetting and acatalytic setting resin, and setting said resin by treating said resinwith at least one of heat and catalyst after emplacement of said resinin said fracture.
 11. A method according to claim 1 wherein saidstabilizing resin is at least one resin selected from the groupconsisting of phenolic resin, urea aldehyde, amine aldehyde, acrylicresin, vinyl resin, allyl resin, alkyl resin, furan resin, polyepoxideresin, polyisocyanate resin, polyester resin, silicone resin, styreneresin, furfuryl alcohol resin, and furfural resin.
 12. A methodaccording to claim 11 wherein said at least one resin is set up using atleast one of heat and a catalyst.
 13. A method according to laim 11wherein said resin and insoluble particles are intimately mixed with oneanother in the absence of carrier fluid to resin wet the insolubleparticles with said resin before said insoluble particles are exposed tosaid carrier fluid.
 14. A method according to claim 13 wherein saidresin and insoluble particles are mixed in the presence of an effectiveamount of at least one coupling agent and in the absence of said carrierfluid.
 15. A method according to claim 1 wherein said stabilizing resinis mixed with said insoluble particles on the earth''s surface beforeemplacement of said insoluble particles into said fracture.
 16. A methodaccording to claim 15 wherein said mixture of resin and insolubleparticles is additionally mixed with carrier fluid before emplacementinto said fracture.
 17. A method according to claim 15 wherein saidresin is mixed with both said insoluble particles and an effectiveamount of at least one coupling agent.
 18. A method according to claim 1wherein said stabilizing resin is at least one of phenol formaldehyde,urea formaldehyde, and phenol furfural.
 19. A method according to claim1 wherein said stabilizing resin is at least one of furfuryl alcoholresin and polyepoxide resin, and said resin is set up by contacting samewith a catalyst after emplacement of said resin and insoluble particlesin said fracture.
 20. A method according to claim 1 wherein saidinsoluble particle slugs contain an effective amount of at least onecoupling agent.